Hitherto, solar systems often have not been equipped with special safety provisions. The solar connection box (also known as solar junction box) provided on each solar module is essentially used to accommodate the mechanical connections of the conductive strips (also known as conductor ribbons) of the solar module and the bypass diodes thereof. Such simple solar modules will supply voltage as soon as they are illuminated.
Typically, the solar modules are series-connected so as to form strings in order to obtain a high string voltage. This voltage of the solar modules connected into strings can amount to several 100 V, and in large systems voltages of about 1000 V or even more may be present, which is a hazardous voltages when being touched. Also, a solar power system optionally comprises a plurality of strings connected in parallel.
Thus, in case of adequate illumination very high voltages might be generated during the installation of solar modules and when electrically connecting them in the string, so that cautious handling and a special contact protection is required. The same applies to maintenance works.
In such simple photovoltaic systems the first possibility for disconnecting the solar generator voltage from the power grid is at the string combiner box. Therefore, in case of damage caused by fire, water, hail or in case of other malfunctions of the solar modules or the string lines there is no way for these simple solar systems to disconnect the part of the photovoltaic system that includes the solar modules and the string lines from voltage.
Safety devices for switching off the individual solar modules in case of fire or faults are known (e.g. DE 10 2009 024 516 A1). However, such solutions are usually only intended for a single emergency switching off.
DE 10 2011 110 682 discloses a junction box which switches from the operating state to a safe state in case of a deviation of the allowed parameters.
As an enhancement of the invention described in DE 10 2011 110 682, the present disclosure relates in particular to a safe shutdown and restart of the photovoltaic system on the condition that the photovoltaic system is able to distinguish between a “real fault” on the one hand and “normal system operation” on the other.